1. Field of the Invention
This invention is directed to a new and useful improvement to an explosive. In particular it is directed to an improved explosive useful as a blasting composition. More particularly it is directed to a blasting composition containing a nitrate and a nonexplosive sensitizer. Even more particularly it is directed to a nonexplosive sensitizer which is carbonaceous. And the improvement resides in the selection of the carbonaceous sensitizer and in particular a hydrocarbon sensitizer. A sensitizer increases the tendency of an explosive material towards detonation. The invention is also directed to an improved method of blasting using the aforementioned blasting composition.
2. Description of the Prior Art
Use of a mixture of inorganic nitrates in an explosive is known, see U.S. Pat. No. 3,367,805. Use of a mixture of inorganic nitrates, including ammonium nitrate, and a combustible organic material is known, see Kirk-Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, 2nd Edition, Vol. 8, section titled "Explosives". Use of a mixture of ammonium nitrate and a certain hydrocarbon, such as diesel fuel, as an explosive is known, see U.S. Pat. No. 3,061,488, or THE SCIENCE OF HIGH EXPLOSIVES, M. A. Cook, publisher American Chemical Society, 1958, ACS Monograph Series No. 139 or Iron Ore Co. of Canada v. Dow Chemical Co., 177 USPQ 33.
A mixture of prilled ammonium nitrate (about 94%) and diesel fuel (about 6%) is a commercial explosive used in large quantities in blasting. The foregoing mixture will be termed AN-DF hereinafter. Blasting refers to industrial and engineering operations wherein mechanical work is performed such as quarrying, ore dislodgement, ditching, excavating, etc., with a low expenditure of time and money. Blasting is used in open pit mining of coal, iron ore, shale oil, tar sands, salt and the like. Details of blasting are discussed in ENCYCLOPEDIA BRITANNICA, Vol. 3, Library of Congress Catalog Card #69-10039.
An AN-DF mixture can be considered an oxygen-balanced mixture for the following reason. When only ammonium nitrate is decomposed the products generally are nitrogen, water and oxygen. Thus by itself ammonium nitrate contains an excess of oxygen. However, if diesel fuel is added to the ammonium nitrate in a sufficient amount so that there is enough carbon and hydrogen to stoichiometrically react with the excess oxygen, the mixture is said to be balanced as to the available oxygen. As a result the formation of the additional gases, that is, CO.sub.2 and H.sub.2 O by the reaction of the carbon and hydrogen of the diesel fuel with the excess oxygen from ammonium nitrate substantially increases the explosive forec of AN-DF mixture compared to just ammonium nitrate.
An AN-DF mixture is often used in the following manner. A hole is drilled into the rock, for example. A suitable amount of the loose, unpackaged AN is poured into the hole followed by a sufficient amount of DF. The resulting mixture is confined and detonated by a suitable blasting cap. Confinement refers to the practice of filling the remainder of the hole with drilled material or other substances such as rock. Confinement increases the efficiency of the explosion.
However, when blasting in a cold environment a problem can occur. The problem occurs because a typical diesel fuel's pour point is about -10.degree. to -20.degree. F. Pour point is a temperature at which an oil ceases to flow. Thus the use of AN-DF mixture can be restricted by the ambient temperature. Furthermore, at a lower temperature, but above a pour point, the diesel fuel's viscosity may be so high so that when it is poured into a drilled hole containing ammonium nitrate it does not properly fill the hole. Also under such conditions the diesel fuel may not flow into the voids between the ammonium nitrate particles. For either one or both reasons, when the AN-DF mixture is detonated, the maximum possible force is not obtained thereby increasing costs.